The present invention relates to a lens assembly for an optical system and more particularly, to a lens assembly that connects a plastic lens to a plastic lens, a plastic lens to a glass lens, or a plastic lens to a barrel. A separation mold surface is set at different sides (outer sides, inner sides or an outer side and an inner side), and a spacer is located between the lenses.
How to reduce factors of reducing the optical resolution and the precision of axial installation is the main issue of the present optical industry. In an optical system, a method of connecting two lenses together is shown in FIG. 1.
A first lens 11 and a second lens 12 are connected with each other by the flat surfaces and their outer periphery are engaged with the barrel 13. The axis of the first lens 11 and the axis of the second lens 12 can be located in alignment with each other when installing the lenses in the barrel by checking the degree of perpendicularity for the flat surfaces to the axes of the first and the second lenses 11, 12, the degree of alignment of the axis of the barrel 13 to the outer peripheries of the first and the second lenses 11, 12, the gap between the barrel 13 and the first and the second lenses 11, 12, and the relative degree of alignment of the contact positions of the barrel 13 and the two lenses 11, 12.
However, when the first and the second lenses 11, 12 includes a plastic lens, there will be some problems when manufacturing. A typical plastic lens is shown in FIG. 2 and consist of four parts in a mold, cavity side sleeve 21, cavity 22, core side sleeve 23 and core 24. Generally, the concentric contact plane is designated to the position 25 and the vertical contact plane is designated to the position 26 or position 27. This arrangement usually leads to some problems.
First, the precise of the shape of the product depends upon the mold and the cavity 22 and the core 24 are machined by two-axle precise lathe which has a precision to 0.1 um and the inner periphery of the barrel is made by way of grinding which has a precision to 1 um. If the positions 25, 26, 27 of the lens are pushed by the molds and if the gate is allowed to be protruded, then the lens can be made by lathe which has a precision up to 2-5 um as shown in FIG. 3. If the positions are pushed by ejection pins 28 and D-shaped cut 29, then electric discharge machining is used which has a precision up to 20 um. Therefore, the optical axes is not easily to be put in alignment with each other.
The primary object of the present invention is to provide a lens assembly of an optical system and which can avoid the difference of optical axes between the outer periphery of lenses and barrel by way of connection between the lenses or between a spacer and a lens. This can increase resolution of the optical system.
The present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention.